Electrochemical properties of TiP2O7 and LiTi2(PO4)3 as anode material for lithium ion battery with aqueous solution electrolyte
Introduction
Lithium ion battery with aqueous solution electrolyte have many advantages such as low cost, easy performance, intrinsic safety and environmental friendly and intrigued many researchers since it has being suggested [1], [2], [3], [4], [5], [6]. This type of battery composes of lithium ion host compounds as electrode materials and aqueous solution as electrolyte. Selection of intercalation materials which de/intercalates Li ions at an appropriate potential is a key factor for the performance of the aqueous battery cell because the stability window of aqueous solution electrolyte is much smaller than non-aqueous electrolyte. There are many compounds with flat charge/discharge curves can be used as cathode materials, such as LiMn2O4, LiCoO2, LiCo0.19Ni0.81O2, LiNi1/3Mn1/3Co1/3O2 and so on [1], [2], [4], [6], [7]. But only a few compounds with flat charge/discharge plateau and proper redox potential being selected as anode was reported [1], [2], [8]. Thus, studies on anode material having somewhat proper redox potential and flat charge/discharge plateau are very important.
Polyanionic compounds with 3D framework structure were fully studied as cathode of lithium battery over the last decades due to quick lithium ion diffusion, stable structure, easy preparation, low cost and so on [9], [10], [11], [12], [13], [14]. However, few reports on electrochemical properties of these compounds in aqueous media were found. Many polyanionic compounds with certain redox potentials looked promising as anode materials for Li-ion battery with aqueous electrolyte and some of them are summarized in Table 1 [9], [12].
In this paper the electrochemical properties of pyrophosphate TiP2O7 and NASICON-type LiTi2(PO4)3 as anode materials in a lithium ion battery with 5 M LiNO3 aqueous electrolyte will be reported due to their lower Li-ion intercalation/deintercalation potentials, which can fully use the stability window of the aqueous electrolyte. The possible reason of capacity fading of the test cells will be discussed.
Section snippets
Experimental
The preparation of TiP2O7 and LiTi2(PO4)3 was based on the scheme described by Sébastien Patoux [11]. For TiP2O7, the mixture of TiO2 and NH4H2PO4 were progressively heated to 1273 K with intermittent grinding sequences. For preparation of LiTi2(PO4)3, TiO2 and NH4H2PO4 and LiH2PO4 precursors were mixed and heated to 573 K at a slow heating rate (2 K/min) to evaporate H2O and NH3, then to 873 K (24 h), and finally to 1273 K (48 h). The cathode material LiMn2O4 was commercial available supplied by
Cyclic voltammetry of TiP2O7 and LiTi2(PO4)3 electrodes
The cyclic voltammograms of TiP2O7 and LiTi2(PO4)3 were recorded at room temperature with Pt sheet as counter electrode and saturated calomel as reference electrode. Fig. 1a shows the CV performance of TiP2O7 in 5 M LiNO3. It can be seen that a pair of Li-ion intercalation and deintercalation peaks can be observed at −0.38 V and −0.26 V (versus SHE), respectively. The hydrogen evolution peak shifts below −0.60 V (versus SHE) due to the over potential effect of the electrodes. Fig. 1b displays the
Conclusion
In this study, aqueous lithium ion cells composed of TiP2O7 or LiTi2(PO4)3 as anodes, LiMn2O4 as cathode and 5 M LiNO3 aqueous solution as electrolyte have been fabricated. The TiP2O7/LiMn2O4 cell delivers about 42 mAh/g at an average voltage of 1.40 and LiTi2(PO4)3/LiMn2O4 cell delivers 45 mAh/g capacity at an average voltage of 1.50 V. Both cells have flat charge and discharge curves, which improve the feasibility of lithium ion battery with aqueous electrolyte in application. While the given
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